1. Field of the Invention
The present invention generally relates to a compact disk (“CD”) player. More particularly, the invention relates to shock protection for a CD player. Still more particularly, the invention relates to shock protection for a CD player that plays audio from a CD containing compressed audio data (e.g., MP3).
2. Background of the Invention
Audio electronics have long included portable devices that permit the user to listen to music or other types of audio. Examples of such devices include battery operated cassette tape players. More recently, compact disk (“CD”) audio players have become extremely popular. A CD disk comprises a relatively flat, round disk that is approximately 4.5 inches in diameter. The information stored on a CD disk is stored in a digital format, not analog as for the larger vinyl records used in conjunction with record players.
CDs have several advantages over records. For example, many audiophiles believe the audio quality from a CD is superior to that of records. Further, CDs are smaller than records. Further still, unlike records which are relatively fragile and must be kept clean, CDs are less fragile and susceptible to dirt and other contaminants. Also, CDs can be played using battery operated CD players, whereas records cannot be played in this fashion.
The information stored on a CD is accessed by rotating the CD under a laser beam. The laser is used to read the bits encoded on the CD. Accordingly, most or all CD players, portable or not, have a mechanism to rotate the CD with respect to the laser. When accessing songs from a CD, no device actually touches the rotating CD unlike the stylus that touches the surface of a rotating record. For this reason, CD players are less susceptible to vibrations and other disturbances than are record players. Nevertheless, CD players are not completely immune from shock and vibration. A significant enough jolt to a CD player that is playing a song can cause a disruption in the laser's ability to access the digital data on the CD, thereby causing a temporary cessation of music.
One approach to solving this problem is through the use of a solid state memory buffer. Data is read from the CD and stored in the buffer which is large enough to hold at least several seconds (or tens of seconds, or more) of audio. Audio data is retrieved from the buffer, converted to an analog format and played back through speakers (e.g., headphones) connected to the CD player. If the CD player experiences a jolt, the mechanism reading the disk may be disturbed momentarily, but that mechanical disturbance does not cause an interruption to the purely electronic process of retrieving data from the buffer and playing it through the speakers. Thus, the player buffers ahead of the point in the song that is being played. This type of “shock protection” is currently available in some models of conventional CD audio players.
Buffering ahead between songs is generally easy and straightforward. Tracks on a conventional CD audio disk are generally arranged contiguously. That is, the end of one track is immediately adjacent the beginning of the next track. Thus, a conventional CD audio player having a shock protection buffer simply needs to inform the “CD loader” (which is the mechanism that moves the laser to the appropriate place on the disk) the track number from which to begin playing. From that point on, audio data is read from the CD and placed into the shock buffer and, because the tracks are arranged end-to-end, the process of buffering ahead can easily continue into the next song.
Conventional CD audio disks contain audio in an uncompressed digital format. Recently, the desire to place more songs on a single CD disk has lead to the development of CD “burners” (devices that store information on a disk) which store audio information in a compressed format. A particularly popular format in use today is the “MP3” standard. Because each song is compressed, an MP3-based CD disk can hold many more songs than conventional, uncompressed audio disks.
As with conventional CD audio disks, the desire is also present to guard against mechanical disturbances while playing MP3 disks. Some MP3 players may have a form of shock protection which guards against mechanical disturbances during a song. However, no MP3 player is known to exist which includes shock protection to guard against disturbances which occur between songs. It is generally known and believed that once an MP3 player finishes playing a song, the MP3 player begins searching for and loading the next song. If a shock or vibration occurs before the MP3 player has any, or much, of the next song buffered up, there will be a delay before the next song can begin to play while the player waits for the mechanical disturbance to subside and begin or continue buffering the next song. MP3 players known to exist today do not provide shock protection to ensure the continuous playing of the next song once the current song finishes.
Conventional MP3 players also are generally only capable of keeping track of and playing one song at a time. That is, such an MP3 player retrieves compressed audio data from the disk and stores it in an internal memory buffer, but only does so for the current song being played. Once the current song is finished playing, at that time the player determines the location on the disk of the next song to be played and begins buffering that song. Although generally acceptable, this process can result in an annoyingly long time between songs while the player's laser is repositioned to the beginning of the next song on the disk. Further, skipping ahead to the next song or back to the beginning of a previous song is fairly slow because the next song or previous song is not present in the player's memory buffer. Instead, the player will have to move the laser head to begin retrieving the desired data from the next/previous song. A solution to this problem also is desirable.